The present invention is related to a non-instantaneous interrupt handover method and an apparatus capable of realizing such a non-instantaneous interrupt handover in a mobile communication system.
In mobile communication systems with using the CDMA (code division multiple access) system, non-instantaneous handover is realized. For instance, wireless (radio) interfaces are defined based upon the EIA/TIA/IS-95 standard as the portable telephone standard system in USA. Similarly, this EIA/TIA/IS-634 defines interfaces between base stations and a mobile switching center.
In these mobile communication systems, the soft handoff or soft handover techniques have been employed as the service area switching techniques during communications. In this soft handover technique, a plurality of communication paths are set at the same time between mobile stations and a mobile switching center, and the same communication data is transmitted/received via a plurality of these communication paths. Data having a low error rate is selected, or the same communication data is synthesized with each other on the reception side, so that the data communication with the low error rate is performed. As a consequence, when the channels are switched during the handover, no discontinuity is produced in the channel under use. Thus, no data drops out, and the handover can be realized without any instantaneous interrupt.
However, the above-described prior art technique owns such an initial condition that the data transfer operation in the mobile communication system is carried out in the STM system (synchronous transfer system). For instance, when the synchronization of the frames containing the respective data is maintained in the transfer path between the base stations and the mobile switching center, the frames are transmitted/received only in the specific timing. As a result, the control unit of the mobile switching center merely makes up the relationship between the specific slot and the connection in the transfer path, but need not especially perform the synchronizations in unit of slot and frame during the transmission/reception operations. As a result, even the soft handover is initiated, the data of the respective slots received at the same time, or the specific timing different from each other can be compared with each other and can be selected. Even when the same data is transmitted to each of the plural base stations, if the same data are duplicated and the duplicated data are transmitted by way of the slots for the handover, than the data of the corresponding slot are synthesized, and selected on the side of the base station, or the mobile stations. Thus, the non-instantaneous handover (soft handover) can be readily realized.
On the other hand, one proposal has been made so as to increase the line utilization efficiency by using ATM (asynchronous transfer)-processing having the above-described transfer path and to transfer each of the above-described data by using the ATM cells.
Even when this asynchronous system is employed in the transfer path, there is a first problem that the continuity of the information during the handover must be maintained.
Also, when the above-described transfer path is ATM-processed, as previously described, the relationship between the transmission/reception timing, the connection, and the channel cannot be exclusively specified.
There is a second problem. That is, in the mobile switching center, either the cell or the frame should be identified which contains the same data related to the same handover from a plurality of data received in the mutually different asynchronous timing from the base stations.
Also, there is a third problem. That is, the connection is specified in unit of the cell, or the frame received from the base station, and the judgment is made as to whether or not the handover is initiated in connection therewith. These comparing process and selecting process must be sequentially carried out in unit of the cell, or the frame.
Furthermore, there is a fourth problem. That is, if the handover is initiated, then either the cells or the frames to be transmitted to the base station are duplicated. Thereafter, these duplicated cells or frames should be transmitted at the same time in such timing that the delays and the flickers determined based on the negotiations with the base stations are minimized.